With the prosperous development of 3C industry for the sake of pursuing the fashionable trend of the market, the current appearance of the 3C apparatus must be designed as tiny as possible and the surface thereof should be polished as mirror-like as possible, so that the requirement of the mold for producing those good-looking case of those 3C products must also meet the preceding requirement as well. In the same time, it also has to further satisfy the demands for maintaining high productivity, extending the duration of mold, and cost down. The most frequently used machining scheme for machining the mold surface is the micro electrical discharging machining (micro-EDM) that is used to be classified as a contact-less type machining. Since while the discharging process is being performed the electrodes used in the process does not contact with the work-piece, so that the surface of work-piece would thus not be influenced by the cutting action or the residual stress over the surface as the conventional contact type machining. Therefore, the application of micro-EDM scheme would not be restricted by the mechanical characters of material, such that it could be applied to machine the extremely hard material and to machine the hardly-cut material. Essentially, the micro-EDM scheme provides the outstanding machining characters and would not be limited by the surface shape of material. In this respect, the scheme is able to machine the object with very thin, slight and tiny volume, complex surface or curve shape. However, numerous micro-craters, cracks and recasted layers induced during the discharging process in the EDM scheme might spread all over the surface of machined object, and the machining quality of surface is therefore influenced, which causes the surface roughness of machine object fails to achieve the anticipative criterion. So majority of numbers of research aim to improve the micro-EDM scheme, which are focused on decreasing the discharging energy, diminishing the electrical current pulse, reducing the duration period of discharging, adding the extra auxiliary powders, or trying the newly electrode material, so as to resolve the issue above the poor surface roughness after performing the micro-EDM scheme. However, even though one could adaptively change and optimize the machining parameters or other conditions in the process, for a single process, it always has its own inherent limitation, which is inevitably unable to break through the inherent limitations. Thus, for a conventional EDM scheme, the machined surface of object should be subsequently polished as a post-process, so as to reach the precise and fine requirements for mold in 3C industry. There are many kinds of polishing process, such as the ionized grit polish, the immobilized grit polish and the grit-less polish. However, no matter which kind of polish is quite complicated and trivial, and is usually time-demanding and costs expansive. Besides, since the work-piece has to be further moved to the polishing base after machining process, it will become a tough issue to be overcame regarding how to precisely locate and position the work-piece on the polishing base in order to maintain the requirements as aforementioned.
A better way to thoroughly eliminate the preceding inherent limitation is to incorporate several different polishing processes into EDM process, so as to take from the long to add to the short. At present, the known polishing scheme to be incorporated into the micro-EDM scheme includes the Electropolishing scheme, the Electrophoretic deposition scheme, the Magnetic abrasive finishing scheme, and the ultrasonic vibration scheme etc. The advantages and the disadvantages of aforementioned polishing schemes are briefly introduced as follows: (1) the Electropolishing scheme adopts the special electrolyte fluid different from the general EDM fluid and is unable to incorporate into the EDM together, and furthermore, during polishing, since the air bubble passivation layer is involved in, the process thus becomes unstable and the polished shape is prone to be rounded; (2) for the Electrophoretic deposition scheme, the composite strength of deposited layer should be controlled, and the deposited thickness is easily influenced by the shape. The scheme is therefore unable to polish the work-piece having complex shape with large curvature. Further, since the strong acid electrolyte and the assisted electrodes are needed for performing the scheme, the process would become complicated; (3) for the Magnetic abrasive finishing scheme, it applies a flexible magnetic polishing brush, but the magnetic field is hardly controlled and the required equipments are complicated and also hardly controlled; and (4) for the ultrasonic vibration scheme, the abrasive grits are not easily loaded into the abrasive region which causes the efficiency of polishing got worse. Further the relative vibration existing between the polishing equipments and the work-piece would reduce the precision.
To overcome the mentioned drawbacks of the prior art, a surface treatment method and device thereof are provided.